While most species of fish are edible, there are some that just shouldn't be consumed. Most reef species can cause ciguatera, which comes from a neurotoxic, dynoflagellate algae often found on dead and dying coral. Some species of fish, parrot-fish in particular, feed upon the algae, which does not pose a threat to them. Barracuda often predate upon the slow-moving parrot-fish, thus the toxin is passed on to the predator. For some strange reason, though, the barracuda are not effected by the toxin, but if you were to consume either the barracuda or the parrot-fish you would have a good chance of contracting the disease, which can be fatal. Most of the time, those that have contracted the disease experience some nasty stinging sensations, severe gastrointestinal pain, horrendous bouts of diarrhea, vomiting, dehydration, and in more severe cases, CNS paralysis that could lead to death if untreated.
In Chesapeake Bay, the waters are so polluted the state has published consumption advisories which can be found at http://www.mde.state.md.us/programs/...ies%202011.pdf
Most tunas are relatively safe to consume, but again, because of the high levels of mercury found in the fatty tissue of the fish, the portion size should be limited to about 8 ounces a week at most. Same holds true with king mackerel (also known as kingfish in tropical waters), bluefish, Atlantic croaker, Spanish mackerel, cero mackerel, and any other oily species of fish.
Tautog, often referred to as poor man's lobster, can be found from Virginia north to Maine, and once you learn how to catch them, you could just about live on them without any fear of contaminants. The taste is absolutely fantastic, and they're available year round at the inshore and offshore wrecks.
In tropical waters, French and Flannel Mouth grunts, some measuring to 15 inches, are a real treat. Again, pretty safe to eat, very tasty when dipped in beer batter and pan fried to a golden brown and served with tartar sauce.
Somewhere in my stacks of books I have a book called Dangerous Marine Animals, and it lists those species that are highly toxic and provides lots of photos. I'll try to dig up a link on the Internet for the book.